Yield secondary electron

Yield, secondary electron The number of electrons emitted from a surface per incident electron or incident ion. The secondary electron yield for electron bombardment is much higher than for ion bombardment. 

Electron multiplier. A device to multiply current in an electron beam (or in a photon or particle beam after conversion to electrons) by incidence of accelerated electrons upon the surface of an electrode. This collision yields a number of secondary electrons greater than the number of incident electrons. These electrons are then accelerated to another electrode (or another part of the same electrode), which in turn emits secondary electrons, continuing the process. 

These signals can be used to form complementary images. As the beam current is increased, each of these currents will also increase. The backscattered electron yield 11 and the secondary electron yield 8, which refer to the number of backscattered and secondary electrons emitted per incident electron, respectively, are defined by the relationships ... 

Mdissociates as a positive ion. Conversely, the enhanced ion yields of the cesium ion beam can be explained using a work function model, which postulates that because the work function of a cesiated surface is drastically reduced, there are more secondary electrons excited over the surface potential barrier to result in enhanced formation of negative ions. The use of an argon primary beam does not enhance the ion yields of either positive or negative ions, and is therefore, much less frequently used in SIMS analyses. 

In radiation chemistry, the track effect is synonymous with LET variation of product yield. Usually, the product measured is a new molecule or a quasi-stable radical, but it can also be an electron that has escaped recombination or a photon emitted in a luminescent process. Here LET implies, by convention, the initial LET, although the actual LET varies along the particle track also, the secondary electrons frequently represent regions of heterogeneous LET against the background of the main particle. 

The yield of free ions in the radiolysis of dienes is very similar to those found for monoalkenes (G = 4.0-4.2)72. Freeman and coworkers73 measured the yield of the free ions (Gg) and the secondary electron penetration (i>Gp) in radiolysis of unsaturated hydrocarbons. Some of the data are given in Table 1. It can be seen that the yield of the free ions is considerably smaller for the dienes studied. Also, the secondary electron penetration is smaller for the dienes, all of them having a similar value (3.9-4.4 nm). 

TABLE 1. Yield of free ions (Gfi) and the secondary electron penetration (hop) for radiolysis of unsaturated hydrocarbons... 

Most of the energy associated with an incident x-ray or y-ray is absorbed by ejected electrons. These secondary electrons are ejected with sufficient energy to cause further ionizations or excitations. The consequences of excitations may not represent permanent change, as the molecule may just return to the ground state by emission or may dissipate the excess energy by radiationless decay. In the gas phase, excitations often lead to molecular dissociations. In condensed matter, new relaxation pathways combined with the cage effect greatly curtail permanent dissociation. Specifically in DNA, it is known that the quantum yields for fluorescence are very small and relaxation is very fast [6]. For these reasons, the present emphasis will be on the effects of ionizations. 

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